Like Earth, Mars has ice caps at its poles. Water reaches the poles as vapor and is frozen into thin layers that build up thick deposits. Mixed with this water is dust picked up by the wind, so the caps have bright and dark layers of "clean" and "dirty" ice. During winter at each pole, temperatures are so low that carbon dioxide freezes from the atmosphere and forms additional layers of "dry ice." Much water is also trapped as permafrost surrounding the polar regions.
Like Earth, Mars spins on an axis tilted about 25 degrees from its orbital plane. Mars has no large satellite like the Moon, just its two small moons Phobos and Deimos. As a result, the tug of gravity from the Sun and the large planets causes a slow wobble in the tilt, or obliquity, of its axis. During periods of higher obliquity, the atmosphere is thicker, dust storms are more intense, and water now trapped at the poles moves to the equatorial region to form mountain glaciers. Many glacial landforms from the last time this occurred can still be seen on Mars. It’s not surprising, that Martian ice and snow tend to be dusty, more so than ice or snow on Earth. Researchers from two universities in the U.S. announced a new study showing just how dusty Mars ice really is.